I have finished the project I have started at the KOS. It is an extension point that allows you to implement own authentication methods for the KREST nodes. It is available in the nightly build. The extension point ID is com.cenix.jerseyauth.custom.
being a Knime user and not a developer, I was wondering if anyone has already implemented a method to use NTLM authentication (for SharePoint 2013) in REST nodes?